What Are Glazing Packers? Types, Sizes, and Common Uses (Installer’s Guide)
When installing windows and doors, ensuring that the frame is level, plumb, and supported is essential for long-term performance. One of the simplest but most important tools in the process is the glazing packer—also known as a glazing shim or window packer.
In this guide, we’ll explain exactly what glazing packers are, why they are needed, the different types and thicknesses available, and how installers use them in real-world situations.
What Are Glazing Packers?
Glazing packers are small, durable plastic spacers used during the installation of windows, doors, and glazed units.
They help ensure that the frame and glass are correctly positioned, level, supported, and protected from movement.
Professional installers use packers to:
- Support the weight of the glass
- Prevent the unit from slipping, bowing, or resting directly on the frame
- Maintain correct drainage and ventilation channels
- Align frames so they sit square inside the aperture
- Prevent pressure points that can crack or stress the glass
- Stop the sash from dropping over time
They form a crucial part of best practice glazing installation across the UK.
Why Do Installers Use Glazing Packers?
Glazing packers solve several very common installation problems:
1. To keep the window or door square
Frames can twist or bow if not correctly packed. Packers maintain correct geometry.
2. To distribute weight evenly
Double-glazed units are heavy. Packers ensure that weight is not concentrated in one area, which could lead to stress cracks.
3. To maintain drainage
Many uPVC window systems rely on clear drainage pathways. Packers lift the glass slightly to let water drain away as designed.
4. To prevent movement over time
Without packers, a glazed unit may drop after a few months, causing:
- doors to rub
- windows to jam
- gaps letting in draughts
- failed locks or misaligned keeps
5. To comply with UK industry practice
Colour-coded plastic packers are now the standard across the glazing industry for accuracy and consistency.
Types of Glazing Packers
Glazing packers come in several forms. The type used depends on the application and the kind of frame (uPVC, aluminium, timber) being installed.
1. Flat Packers
These are the most commonly used packers.
They have a simple rectangular shape and a precise thickness.
Uses:
- leveling frames
- supporting glazing units
- spacing hinges
- correcting gaps
Available in multiple thicknesses (usually colour-coded).
2. Wedge Packers
Wedge packers (also called tapered packers) have a sloped profile.
Uses:
- fine adjustments where a small incremental lift is needed
- correcting uneven cavities
- aligning frames where surfaces are not perfectly square
Ideal for installers who need micro-adjustments that flat packers cannot achieve alone.
3. Bridge Packers
Bridge packers have a central cut-out or raised “bridge” which allows them to sit over fixing screws or pinched areas.
Uses:
- applications where screws are present under the packer
- avoiding compression on screw heads
- supporting loads without distortion
Commonly used in uPVC windows where screws run close to the glazing area.
4. Mixed & Assorted Sets
Most installers keep a selection box that includes multiple sizes of:
- flat packers
- wedge packers
- bridge packers
Useful for on-site adjustments where frame gaps differ from window to window.
Glazing Packer Sizes and Thicknesses
Packer thicknesses follow industry-standard colour coding for quick identification.
Typical thicknesses include:
| Colour | Thickness |
|---|---|
| Black | 1 mm |
| Green | 2 mm |
| White | 3 mm |
| Blue | 4 mm |
| Red | 5 mm |
| Yellow | 6 mm |
| Brown | 10 mm |
These are the most common, but installers may also use:
- 8 mm
- 12 mm
- 15 mm
depending on the frame depth and manufacturer.
Note: Colour coding can vary slightly between manufacturers, but the above table represents the widely used UK standard.
Where Are Glazing Packers Used?
1. Window Installation
Packers are used to:
- level uPVC or aluminium frames
- keep sashes square
- support double- or triple-glazed units
- maintain drainage gaps
- reduce stress on glass
Correct packing ensures smooth operation of the window for years.
2. Door Installation
Glazed doors can be heavy, especially patio and composite doors.
Installers use packers to:
- align the door frame in the opening
- support glazing panels
- prevent the door from dropping
- maintain even reveal lines
3. Timber Frames
Packers help avoid moisture absorption and keep the unit raised from the timber.
4. Construction & Joinery
Beyond glazing, packers are often used to:
- level kitchen units
- fit cabinets
- align stud walls
- level flooring or decking
- fix frames and architraves
Installers keep packers in their toolkit for all alignment tasks.
Benefits of Using Proper Glazing Packers
- Stronger structural support
- Correct alignment
- No frame distortion or bowing
- Reduced risk of glass cracking
- Smooth window/door operation
- Compliance with good UK glazing practice
- Prevents callbacks and warranty issues
For professionals, using the right packers is a small cost that prevents expensive future problems.
Frequently Asked Questions
Do all windows need glazing packers?
Yes. Any glazed unit—uPVC, aluminium, or timber—should be properly packed to support the weight and maintain alignment.
Can you pack a window with wood or cardboard?
No.
These materials absorb moisture, compress, and cause failures.
Only proper plastic glazing packers should be used.
Can packers fix a dropped or stiff window?
Yes, in many cases a window that has dropped can be corrected by re-packing the glazing unit.
Do colour codes matter?
Yes. They ensure consistent measurable thicknesses so installers can work accurately.
Final Thoughts
Glazing packers may be small, but they are essential for correct window and door installation. The right packer ensures structural integrity, smooth operation, proper drainage, and long-term performance.
If you’re looking for colour-coded, installer-approved packers, explore our full range here: